The present invention relates to an optical device and an optical sensor.
In recent years, for further densification of optical disk information recording media, an optical device, which outputs a near-field light (including an evanescent wave), has attracted attention as an optical device capable of obtaining light of an extremely minute spot size. Moreover, with regard to the utilization of near-field light, there are expected applications to a wide variety of technological fields. As a prior art, there is the optical device described in Japanese Patent Laid-Open Publication No. 2000-22277. This prior art obtains light of an extremely minute spot size by providing a wave front transforming portion that has a pinhole of an aperture diameter smaller than the wavelength of light at the laser light emitting end face of a semiconductor laser device, transforming the laser light into an evanescent wave via this pinhole and generating a near-field in the vicinity of the pinhole.
The intensity of the evanescent wave has a dependency on the polarization direction of light incident on an interface. There can be obtained an evanescent wave of a size about four or more orders of magnitude greater in terms of an intensity ratio when light of the polarized light that has an electric field vector component perpendicular to the interface where the evanescent wave is generated (hereinafter referred to as the p-polarized light) is made incident than when light of the polarized light that has an electric field vector component parallel to the interface (hereinafter referred to as the s-polarized light) is made incident. However, according to the aforementioned conventional optical device, the electric field vector of the laser light becomes roughly parallel mainly to a reflection end face that serves as the interface in the semiconductor laser device that is performing laser oscillation. That is, the laser light of the s-polarized light is mainly made incident on the reflection end face. Accordingly, there is a problem that the transformation efficiency of the laser light into the evanescent wave is poor. There is a further problem that no resonance effect of the near-field light by a surface plasmon can be obtained by the aforementioned prior art since the surface plasmon excitation in a metal film, a metal particle or the like can be generated only by the p-polarized light.